Generally, by the term skin aging is meant a physiological phenomenon which involves a physiological aging with getting old and photoaging due to exposure to sunlight (ultraviolet rays) influencing each other. Currently, attention is being paid to relationship between the latter, i.e., photoaging, and wrinkled skin, rough skin, spots, and the like. That is, it has been known that continued exposure to sunlight (ultraviolet rays) increases deep wrinkles in the face or neck and further renders the skin dry and rough, and causes pigment deposition such as spots, freckles, and the like. Therefore, troubles in the skin due to photoaging has become an issue.
Hitherto, in order to prevent the damages to the skin due to ultraviolet rays, cosmetics (sun-screen or sun-protecting cosmetics) containing various ultraviolet absorbents, scattering or shielding agents, such as titanium oxide, zinc oxide, p-methoxycinnamic acid esters, p-aminobenzoic acid esters, and the like, have been developed and put into use. However, it is difficult to protect the skin from abundant exposure to sunlight despite the use of such cosmetics. Further, it has been known that external application of all trans-type retinoic acid is effective as a method of improving the above-described photoaging (see Methods in Enzymology, Vol. 190, p. 352-360 (1990)). However, use of this method is open only to doctors from the viewpoint of safety so that there has been demanded a development of a photoaging inhibitor and skin-care preparations which are highly effective and safe.
Accordingly, in order to meet the above-described demand, there have been used triterpenoids from plant origins, such as ursolic acid and oleanolic acid, or their derivatives such as esters, in photoaging ameliorating agents, cosmetics, externally applied skin agents and the like. However, triterpenes used as raw materials for these substances are very low in their content in plants so that there occur problems that blending them in amounts which assure sufficient effects is expensive and that it is difficult to assure a sufficient supply of them. Therefore, there has been a demand for the development of triterpenoid compounds that can exhibit sufficient effects in small amounts among the triterpenoid compounds which are highly safe, have photoaging preventing and ameliorating effect and are excellent in the skin beautifying effect.